A container used to drip a liquid contained therein such as an eye dropper employs a liquid delivery device 90 installed at a mouth 92a of a container body 92 such as one shown in FIG. 13(a), (b). The delivery device 90 discharges the content liquid in the form of drop 94 through an outlet orifice 91 when the container body 92 is depressed.
With respect to the delivery device 90 shown in FIG. 13, however, since outside air is taken in through an outlet opening 93 so as to restore the container body 92, that has been deformed by depressing, into the original shape after discharging the liquid, there has been such a problem that microorganisms such as bacteria and dust deposited on the outlet opening 93 enter the container body 92 when the liquid (ophthalmic solution, for example) 95 that has remained in the outlet opening 93 flows back into the container body 92 (refer to FIG. 14(a), (b)). In case the container is an eye dropper, in particular, it is very likely that such a problem occurs as the outlet opening 93 can easily catch microorganisms and dust through contact with cornea and/or eye lid.
Since the entry of microorganisms and dust into the container body may cause the liquid contained therein to decay or deteriorate, the liquid (ophthalmic solution) contained in the eye dropper contains an antiseptic agent such as benzalkonium chloride or parabens (paraoxybenzoate esters) mixed therein. However, there remain such problems that it is difficult to prescribe a proper composition containing an antiseptic agent depending on the type and purpose of the liquid contained in the container, and that the antiseptic agent added to the ophthalmic solution may cause a side effect such as allergy in the user.
For these reasons, it has been studied to eliminate or reduce the use of antiseptic agents. For example, disposable eye droppers comprising small container that contains a very small quantity of ophthalmic solution and is sealed without antiseptic agent added thereto have been provided. However, disposable eye droppers have been restricted to particular applications and are not used for general purpose due to the disadvantage in terms of cost.
Patent Document 1(Japanese Unexamined Patent Publication No. 2002-80055) discloses a delivery container provided with a filter that employs a so-called delamination bottle having an outer layer (outer container) and an inner layer (inner container) which is provided delaminatably on the inside of the outer layer. Since this delivery container prevents outside air from flowing into the container through the outlet opening after delivering the content liquid, contamination of the liquid in the container by bacteria, dust and the like can be prevented. However, this container has a problem of high manufacturing cost since it is necessary to provide an inner container that is easily deformed according to a change in the inside pressure of the container caused by the delivery of the liquid.
Patent Document 2(Japanese Unexamined Patent Publication No. 2001-179017) and Patent Document 3 (Japanese Unexamined Patent Publication No. 2001-206454) disclose antibacterial containers having a porous filter that has pores small enough to prohibit the passage of bacteria and dust and is disposed at the outlet opening thereof. In this case, however, when the porous filter dries up after being wetted by a liquid medicine or the like, there is a possibility that the filter is choked with the solute contained in the liquid. When the content of the container is a suspension, the problem of choked filter is more likely to occur. Moreover, while the containers described in Patent Documents 2 and 3 employ the porous filters made of sintered metal or sintered resin, in which case fine particles of the sintered material may be mixed in the liquid so as to be delivered therewith out of the container.
Thus there have been demands for a delivery container such as eye dropper that can prevent the content liquid (liquid medicine) from flowing back through the outlet orifice, and achieve aseptic delivery (dripping) of the content liquid.